The vast majority of the county population lies in and around the city of Tucson (2011 city population: 525,796), filling much of the eastern part of the county with urban development. Tucson, Arizona's second largest city, is a major commercial and academic center. Other urban areas include the Tucson suburbs of Oro Valley (population 41,335), Marana (population 35,232), Sahuarita (population 25,458), and South Tucson (population 5,695), a large ring of unincorporated urban development, and the growing satellite townGreen Valley. The rest of the county is sparsely populated; the largest towns are Sells, the capital of the Tohono O'odham Nation, and Ajo in the far western region of the county.